Efforts were begun to adapt MAPREC as a potentially useful regulatory method for control of consistency of production of live viral vaccines other than OPV. High-passage samples of yellow fever virus vaccine (YFV) and of a cloned Jeryl-Lynn strain of mumps virus were obtained and subjected to sequence heterogeneity assay. Two nucleotide differences were identified in serially passaged YFV, and amounts of those mutations in various passage levels, and in commercial batches of YFV vaccine are now being quantified by MAPREC. A nucleotide sequence difference between the original strain of YFV and the passaged virus stocks was detected. It utility for monitoring consistency of YFV is now being investigated. A new mumps candidate vaccine strain, derived from the licensed Jeryl-Lynn vaccine strain, was completely sequenced, and that sequence was compared to another mumps strain, the nucleotide sequence of which has been published. A high passage of the new Jeryl-Lynn strain was also sequenced. Serially passaged preparations of mumps vaccine viruses are now being compared to unpassaged vaccine virus preparations to identify unstable genomic sites suitable for monitoring the consistency of mumps vaccine production. A MAPREC test for quantification of sequence heterogeneities in Mumps vaccine batches was developed. The preliminary results of studies with mumps vaccine strains were presented by a Guest Research Scientist at a meeting organized by his sponsoring organization.